Method and system for operating an engine turbocharger

ABSTRACT

A system and method for operating an engine turbocharger is described. In one example, the turbocharger is rotated in different directions in response to operating conditions. The system and method may reduce engine emissions.

BACKGROUND/SUMMARY

It may be desirable to reduce engine emissions at time of enginestarting so that average engine emissions over a driving cycle may bereduced. One way to improve engine emissions at the time of starting isto operate an engine rich and to supply air to an exhaust system coupledto the engine. Such operation allows engine exhaust gas constituents tobe oxidized in the exhaust system. In particular, hydrocarbons in theexhaust gases may be oxidized when combined with air introduced to theexhaust system. The oxidizing hydrocarbons release heat that may betransferred to an after treatment devices in the exhaust system. Theheat transfer reduces an amount of time that it takes for the aftertreatment device to reach operating temperature. Consequently, the aftertreatment device may begin to convert exhaust constituents to moredesirable compounds sooner after engine starting, thereby reducingengine emissions. However, systems that inject air into an engineexhaust system increase system cost and may be less reliable thansystems that do not inject air into engine exhaust.

The inventors herein have recognized the above-mentioned limitations andhave developed a method for operating an engine, comprising: rotating aturbocharger coupled to the engine in a first direction to increase atime engine exhaust gases are in an exhaust manifold; and rotating theturbocharger in a second direction different than the first direction toincrease engine output torque.

By rotating a turbocharger in two different directions, it may bepossible to both improve engine emissions and engine power output. Forexample, after an engine start, a turbocharger may be rotated in a firstdirection opposed to a direction that engine exhaust gases drive theturbocharger so that exhaust gases experience a greater latency time inthe engine exhaust manifold. A greater latency time may allow for morecomplete oxidation of exhaust gases in the exhaust manifold so thatengine emissions may be improved. Additionally, rotating theturbocharger in a first direction opposed to a direction theturbocharger rotates when acted upon by exhaust gases exiting enginecylinders may increase exhaust back pressure which may also help toimprove engine emissions during some conditions. Subsequently, theturbocharger may be rotated in a second direction that pressurizes airentering the engine to increase engine performance.

The present description may provide several advantages. In particular,the approach may reduce engine emissions during an engine cold start.Further, the approach may reduce fuel consumption by reducing catalystlight off time so that an amount of time the engine is operated lessefficiently may be reduced. Additionally, the approach may provide for amore reliable way to reduce engine emissions as compared to systems thatutilize secondary air injection to the exhaust system.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic depiction of an engine;

FIGS. 2 and 3 show example devices for changing rotational direction ofa turbocharger;

FIGS. 4 and 5 show example conditions when a turbocharger turbine isrotated in a direction opposed to a direction the turbocharger turbinerotates when driven via engine exhaust gases exiting engine cylinders;

FIGS. 6 and 7 show simulated engine cold starting sequences; and

FIG. 8 shows an example method for operating a turbocharger.

DETAILED DESCRIPTION

The present description is related to operating a turbocharger. In oneexample, a turbocharger turbine rotates in a direction determined byexhaust flow from engine cylinders. In another example, the turbochargerturbine rotates in a direction opposite the direction the turbinerotates when driven by engine exhaust gases. The approach may improveengine emissions by improving oxidation of exhaust gases in an exhaustmanifold. One example system is shown in FIG. 1. The engine andturbocharger may be operated to provide the sequences of FIGS. 6 and 7via the method shown in FIG. 8. Example turbochargers are shown in FIGS.2 and 3. FIGS. 4 and 5 show exhaust flow in the vicinity of aturbocharger according to the method of FIG. 8. Engine startingsequences according to the method of FIG. 8 are shown in FIGS. 6 and 7.

Referring to FIG. 1, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 1, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 30 and cylinder walls 32 with piston 36 positionedtherein and connected to crankshaft 40. Combustion chamber 30 is showncommunicating with intake manifold 44 and exhaust manifold 48 viarespective intake valve 52 and exhaust valve 54. Each intake and exhaustvalve may be operated by an intake cam 51 and an exhaust cam 53. Theposition of intake cam 51 may be determined by intake cam sensor 55. Theposition of exhaust cam 53 may be determined by exhaust cam sensor 57.

Fuel injector 66 is shown positioned to inject fuel directly intocylinder 30, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector 66delivers liquid fuel in proportion to a pulse width provided bycontroller 12. Fuel is delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, fuel pump, and fuel rail (not shown).

Intake manifold 44 is supplied air by compressor 162. Exhaust gasesrotate turbine 164 which is coupled to shaft 161, thereby drivingcompressor 162. In some examples, a bypass passage 77 is included sothat exhaust gases may bypass turbine 164 during selected operatingconditions. Flow through bypass passage 77 is regulated via waste gate75. Further, a compressor bypass passage 86 may be provided in someexamples to limit pressure provided by compressor 162. Flow thoughbypass passage 86 is regulated via valve 85. In this example, a firstmagnetic field is provided by windings, or alternatively permanentmagnets, 170 coupled to shaft 161, and winding 171 provides a secondmagnetic field when supplied current via controller 12. The two magneticfields can rotate or hold shaft 161 so as to control the rotationaldirection of compressor 162 and turbine 164. In addition, intakemanifold 44 is shown communicating with central throttle 62 whichadjusts a position of throttle plate 64 to control air flow from engineair intake 42. Central throttle 62 may be electrically operated.

Distributorless ignition system 88 provides an ignition spark tocombustion chamber 30 for igniting an air-fuel mixture via spark plug 92in response to controller 12. In other examples, the engine may be acompression ignition engine without an ignition system, such as a dieselengine. Universal Exhaust Gas Oxygen (UEGO) sensor 126 is shown coupledto exhaust manifold 48 upstream of catalytic converter 70.Alternatively, a two-state exhaust gas oxygen sensor may be substitutedfor UEGO sensor 126.

Converter 70 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 70 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 1 as a conventional microcomputerincluding: microprocessor unit 102, input/output ports 104, read-onlymemory 106, random access memory 108, keep alive memory 110, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 112 coupled to cooling sleeve 114; a position sensor134 coupled to an accelerator pedal 130 for sensing accelerator positionadjusted by foot 132; a measurement of engine manifold pressure (MAP)from pressure sensor 122 coupled to intake manifold 44; an engineposition sensor from a Hall effect sensor 118 sensing crankshaft 40position; a measurement of air mass entering the engine from sensor 120(e.g., a hot wire air flow meter); and a measurement of throttleposition from sensor 58. Barometric pressure may also be sensed (sensornot shown) for processing by controller 12. In a preferred aspect of thepresent description, engine position sensor 118 produces a predeterminednumber of equally spaced pulses every revolution of the crankshaft fromwhich engine speed (RPM) can be determined.

In some examples, the engine may be coupled to an electric motor/batterysystem in a hybrid vehicle. The hybrid vehicle may have a parallelconfiguration, series configuration, or variation or combinationsthereof. Further, in some embodiments, other engine configurations maybe employed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 54 closes and intake valve 52 opens. Air isintroduced into combustion chamber 30 via intake manifold 44, and piston36 moves to the bottom of the cylinder so as to increase the volumewithin combustion chamber 30. The position at which piston 36 is nearthe bottom of the cylinder and at the end of its stroke (e.g. whencombustion chamber 30 is at its largest volume) is typically referred toby those of skill in the art as bottom dead center (BDC). During thecompression stroke, intake valve 52 and exhaust valve 54 are closed.Piston 36 moves toward the cylinder head so as to compress the airwithin combustion chamber 30. The point at which piston 36 is at the endof its stroke and closest to the cylinder head (e.g. when combustionchamber 30 is at its smallest volume) is typically referred to by thoseof skill in the art as top dead center (TDC). In a process hereinafterreferred to as injection, fuel is introduced into the combustionchamber. In a process hereinafter referred to as ignition, the injectedfuel is ignited by known ignition means such as spark plug 92, resultingin combustion. During the expansion stroke, the expanding gases pushpiston 36 back to BDC. Crankshaft 40 converts piston movement into arotational torque of the rotary shaft. Finally, during the exhauststroke, the exhaust valve 54 opens to release the combusted air-fuelmixture to exhaust manifold 48 and the piston returns to TDC. Note thatthe above is described merely as an example, and that intake and exhaustvalve opening and/or closing timings may vary, such as to providepositive or negative valve overlap, late intake valve closing, orvarious other examples.

Referring now to FIG. 2, a cross section of a first device for reversingrotational direction of a turbocharger is shown. Turbine 164 is shownmechanically coupled to shaft 161. Compressor 162 is also shownmechanically coupled to shaft 161. Shaft 161 is supported via bearings210.

During engine operation, exhaust gases act on turbine 164 to cause it torotate in a first direction, thereby rotating shaft 161 and compressor162. However, in selected engine operating conditions (e.g., at idlespeed after engine starting), current may flow through winding 171 viacontroller 12 to produce a first magnetic field. A second magnetic fieldproduced by winding, or alternatively permanent magnets 170, isattracted to and/or repelled from the first magnetic field to rotate orhold stationary shaft 161. Applying current to winding 171 allows amagnetic field to rotate shaft 161 in a direction opposite to thedirection shaft 161 rotates when exhaust gas applies force to turbine164.

Referring now to FIG. 3, a cross section of an alternative device 300for reversing rotational direction of a turbocharger is shown. Thecomponents of device 300 that have the same numbers as the components ofthe device shown in FIG. 2 are the same components as shown in FIG. 2,and the components operate as discussed in the description of FIG. 2.

Device 300 includes a hydraulic flow control device (e.g., a valve) 340and a hydraulic pump 342. Hydraulic pump is integrated with shaft 161and may include vanes 343. Shaft 161 may rotate via opening valve 340which allows hydraulic fluid such as oil to enter hydraulic pump 342.Opening valve 340 allows oil to operate on vanes 343 to rotate shaft 161in a direction opposite to the direction shaft 161 rotates when exhaustgas applies force to turbine 164. In one example, hydraulic pump 342 maybe hydraulically driven in a single direction to provide reverse turbinerotation.

Referring now to FIG. 4, example gas flow conditions proximate to aturbocharger when a turbine is rotated in a direction opposite to adirection the turbine rotates when driven via exhaust gases is shown. Inthis example, waste gate valve 75 is in an open state allowing exhaustgases to flow through bypass 77. Exhaust gases ejected from enginecylinders flow in the direction indicated by arrow 402. The engineexhaust gases mix with exhaust gases transported from downstream (e.g.,in the direction of exhaust flow from engine cylinders) turbine 164 asindicated by arrow 408. Turbine 164 supplies exhaust gases to upstreamof turbine 164 in the direction of arrow 406 when rotated in a reversedirection via electromechanical or hydraulic actuator (e.g., the devicesshown in FIGS. 2 and 3). Mixed exhaust gases flow in the direction ofarrow 404 through waste gate valve 75 via passage 77 when waste gatevalve 75 is open as is shown. Exhaust gases exit waste gate 75 and flowtoward atmosphere as indicated by arrow 410 or are recirculated in thedirection of arrow 412. In this example, directions of forward andreverse turbine rotation are as indicated.

Thus, by rotating in a reverse direction via hydraulic or electricmotive force, exhaust gases are drawn through turbine 164 and returnedto upstream of turbine 164. By rotating turbine 164 in a reversedirection, the latency time of exhaust gases upstream of turbine 164 isincreased so that more complete oxidation of exhaust gases may occur.Such an exhaust flow pattern may be created shortly after an engine isrestarted so that exhaust gas oxidation in the exhaust system is morecomplete.

Referring now to FIG. 5, example gas flow conditions proximate to aturbocharger when a turbine is rotated in a direction opposite to adirection the turbine rotates when driven via exhaust gases is shown. Inthis example, waste gate valve 75 is in a closed state stopping exhaustgases from flowing through bypass 77. Exhaust gases ejected from enginecylinders flow in the direction indicated by arrow 502. The engineexhaust gases mix with exhaust gases transported from downstream (e.g.,in the direction of exhaust flow from engine cylinders) turbine 164 asindicated by arrow 508. Turbine 164 supplies exhaust gases to upstreamof turbine 164 when rotated in a reverse direction via electromechanicalor hydraulic actuator (e.g., the devices shown in FIGS. 2 and 3).Substantially zero exhaust flows through bypass passage 77 when wastegate 75 is in a closed state. A small amount of exhaust gas may pass byturbine 164 to downstream of turbine 164 as indicated by arrow 512. Insome examples, waste gate 75 may only be in a closed state for a shortduration so that a sufficient amount of exhaust gases can be evacuatedfrom engine cylinders so that the engine may continue to operate.

Thus, by rotating in a reverse direction via hydraulic or electricmotive force, exhaust gases and/or air may be drawn through turbine 164and returned to upstream of turbine 164. By rotating turbine 164 in areverse direction, the latency time of exhaust gases upstream of turbine164 is increased so that more complete oxidation of exhaust gases mayoccur. Such an exhaust flow pattern may be provided during and shortlyafter engine run-up (e.g., time between when engine speed is betweencranking speed and idle speed.

Referring now to FIG. 6, a simulated engine cold starting sequence isshown. The sequence of FIG. 6 may be provided via the system shown inFIGS. 1-3 executing instructions stored in non-transitory memoryaccording to the method of FIG. 8.

The first plot from the top of FIG. 6 shows engine speed versus time.The Y axis represents engine speed and the X axis represents time. Timeincreases from the left side of the figure to the right side of thefigure. Engine speed increases in the direction of the Y axis arrow.

The second plot from the top of FIG. 6 shows exhaust after treatmentdevice temperature (e.g., catalyst temperature) versus time. The Y axisrepresents exhaust after treatment device temperature and the X axisrepresents time. Time increases from the left side of the figure to theright side of the figure. Exhaust after treatment device temperatureincreases in the direction of the Y axis arrow. Horizontal line 602represents a threshold after treatment device temperature. For example,the after treatment device is operating with an expected level ofefficiency when the after treatment device is above thresholdtemperature 602. The after treatment device is operating with less thanthe expected level of efficiency when the after treatment device is lessthan threshold temperature 602. Trace 603 represents after treatmentdevice temperature when the engine is operated according to the methodof FIG. 8. Trace 604 represents after treatment device temperature whenthe engine is operated not according to the method of FIG. 8.

The third plot from the top of FIG. 6 shows engine torque demand versustime. The Y axis represents engine torque demand and the X axisrepresents time. Time increases from the left side of the figure to theright side of the figure. Engine torque demand increases in thedirection of the Y axis arrow.

The fourth plot from the top of FIG. 6 shows turbine rotation directionversus time. The Y axis represents turbine rotation direction and the Xaxis represents time. Time increases from the left side of the figure tothe right side of the figure. Turbine rotation direction is in reversewhen above line 610 and forward when below line 610. Forward directionfor the turbine is the direction the turbine rotates when exhaustsrotate the turbine and not when the turbine is rotated electrically orhydraulically.

The fifth plot from the top of FIG. 6 shows turbocharger waste gateposition versus time. The Y axis represents waste gate position and theX axis represents time. Time increases from the left side of the figureto the right side of the figure. Waste gate opening amount increases inthe direction of the Y axis arrow.

At time T₀, the engine is stopped and the after treatment devicetemperature is at a low level. The engine torque demand is also low andthe turbine is not rotating. Further, the turbocharger waste gate is ina closed position.

Between time T₀ and time T₁, the engine is started in response to anengine start request as indicated by the increasing engine speed. Theafter treatment device temperature is low, but it begins to increase.The engine torque demand remains at a low level and the turbine is shownnot rotating. However, in some examples, the turbocharger may begin torotate in a reverse direction in response to an engine start request.The turbocharger waste gate remains held in a closed position. However,in some examples, the turbocharger waste gate may be commanded open inresponse to the engine starting request.

At time T₁, the turbine begins to rotate in a reverse direction. Inparticular, the turbine rotates in a direction opposite to a directionthe turbine rotates when driven by exhaust gases leaving enginecylinders. In one example, the turbine rotates in the reverse directionin response to an amount of time after the engine was last stopped andin response to after treatment device temperature. Alternatively, theturbine may be reverse rotated in response to an engine speed beingachieved by the engine after engine start. The after treatment devicetemperature begins to increase and hydrocarbons are oxidized in theexhaust manifold since reversing the turbocharger rotational directionincreases the latency time of exhaust in the engine exhaust manifold.Further, the waste gate remains in a closed position, although aspreviously mentioned, the waste gate may be opened at an earlier time,if desired. The engine torque demand remains at the low level. Exhaustflow at the turbine at time T₁ is as shown in FIG. 5.

At time T₂, the waste gate is commanded open and exhaust gases begin toflow around the turbine as illustrated in FIG. 4. The waste gate may becommanded open in response to an exhaust backpressure level or an amountof time since the engine was last stopped. The after treatment devicetemperature continues to increase and the engine torque command stays ata relatively low level.

At time T₃, the engine torque demand is increased and the waste gate isclosed in response to the increase in torque demand. The engine torquecommand may be increased via a driver or a controller. Additionally,force applied to the turbocharger shaft via an electric or hydraulicdevice ceases in response to the increasing engine torque demand.Further, the waste gate is adjusted to a closed position in response tothe engine torque demand. Consequently, engine exhaust gases cause theturbine rotational direction to change from reverse to forward. Theturbocharger begins to supply pressurized air to the engine after theturbine direction is reversed. Before turbine direction is reversed, thecompressor also rotates in a reverse direction and does not providepressurized air to the engine. In some examples, a compressor bypassvalve may be opened to let air flow to the engine when the compressor isrotating in a reverse direction.

At time T₄, the engine torque demand is reduced to a low value via thevehicle driver or a controller. The engine speed begins to be reducedand the waste gate position partially closes in response to the lowerengine torque request. After treatment device temperature is belowthreshold level 602 at time T₄, but it continues to increase and iteventually exceeds threshold level 602. The turbine direction ofrotation remains forward after the engine torque demand is increased.

In this way, turbine direction of rotation may be reversed and thendriven forward in response to an engine torque request. Rotating theturbocharger in a forward direction allows the turbocharger compressorto supply pressurized air to the engine so that the engine torquerequest may be met.

Referring now to FIG. 7, another simulated engine cold starting sequenceis shown. The sequence of FIG. 7 may be provided via the system shown inFIGS. 1-3 executing instructions stored in non-transitory memoryaccording to the method of FIG. 8. The plots shown in FIG. 7 are of thesame signals as described in FIG. 6. Therefore, for the sake of brevity,the plot and signal descriptions are omitted and the differences betweenthe plots are discussed. Trace 703 represents after treatment devicetemperature for the illustrated sequence according to the method of FIG.8. Trace 704 represents after treatment device temperature when themethod of FIG. 8 is not applied.

At time T₀, the engine is stopped and the after treatment devicetemperature is at a low level. The engine torque demand is also low andthe turbine is not rotating. Further, the turbocharger waste gate is ina closed position.

Between time T₀ and time T₁, the engine is started in response to anengine start request as indicated by the increasing engine speed. Theafter treatment device temperature is low, but it begins to increase.The engine torque demand remains at a low level and the turbine is shownnot rotating. However, in some examples, the turbocharger may begin torotate in a reverse direction in response to an engine start request.The turbocharger waste gate remains held in a closed position. However,in some examples, the turbocharger waste gate may be commanded open inresponse to the engine starting request.

At time T₁, the turbocharger turbine is rotated in a reverse directionvia an electric or hydraulic actuator that acts on a turbocharger shaft.In one example, the actuator is as described in FIG. 2 or 3. The wastegate is initially closed and the engine torque demand is at a low level.The after treatment device temperature begins to increase andhydrocarbons are oxidized in the exhaust manifold as reversing theturbocharger rotational direction increases the latency time of exhaustin the engine exhaust manifold. The turbocharger turbine may be rotatedin the reverse direction in response to an amount of time after enginestop and in response to after treatment device temperature.

At time T₂, the after treatment device reaches threshold temperature602. The after treatment device converts exhaust gas constituents to CO₂and H₂O with a desired efficiency at temperatures above 602. The turbinerotational direction and the compressor rotational direction change froma reverse direction to a forward direction in response to the aftertreatment device reaching the threshold temperature. In particular,supply of energy to rotate the turbine in the reverse direction ceasesand the waste gate is closed so that an amount of exhaust gas acting onthe turbine increases causing turbine rotational direction to change.The engine torque demand remains at a low level.

Thus, in this example where the engine torque demand is low and aftertreatment device temperature reaches threshold temperature 602 beforethe engine torque request is increased, turbine rotation direction isreversed in response to after treatment device temperature.

Referring now to FIG. 8, a method for operating a turbocharger is shown.The method of FIG. 8 may be stored as instructions in non-transitorymemory of controller 12 in the system shown in FIG. 1. Further, themethod of FIG. 8 may provide the operating sequences illustrated inFIGS. 6 and 7.

At 802, method 800 determines operating conditions. Operating conditionsmay include but are not limited to engine speed, after treatment devicetemperature, engine load, engine torque demand, engine temperature,intake manifold pressure, and exhaust back pressure. Method 800 proceedsto exit after operating conditions are determined.

At 804, method 800 judges whether or not a predetermined duration orcondition after engine start request has been met. In one example, thepredetermined duration is an amount of time or a number of combustionevents since the engine was last stopped. In other examples, thepredetermined condition is an engine start request. If the duration orcondition after the engine start request has been met, the answer is yesand method 800 proceeds to 806. Otherwise, the answer is no and method800 returns to 804.

At 806, method 800 judges whether or not an after treatment device(e.g., catalyst or particulate filter) temperature is greater than athreshold level. The threshold temperature level may vary for differentengine operating conditions. For example, the threshold temperature maybe a first temperature for engine starting at a first temperature. Thethreshold temperature may be a second temperature for engine starting ata second temperature, the second temperature greater than the firsttemperature. If after treatment device temperature is greater than thethreshold temperature, the answer is yes and method 800 proceeds to 830.Otherwise, the answer is no and method 800 proceeds to 810.

At 830, method 800 ceases to provide energy to rotate the turbine in areverse direction (e.g., a direction opposed to the direction exhaustgases exiting the engine drive the turbine) and exhaust gases areallowed to rotate the turbine in a forward direction. Additionally, ifthe turbine is rotating in a reverse direction with the turbochargerwaste gate in an open position, the waste gate is commanded closed inresponse to after treatment device temperature, engine torque demand, oran amount of time since the engine was last stopped. Closing the wastegate allows the turbine to switch directions sooner than if the wastegate is allowed to remain open. After the turbine begins to rotate in aforward direction, compressed air is provided to the engine via thecompressor.

At 810, method 800 judges whether or not an engine torque demand isgreater than a threshold. In one example, the engine torque demand mayoriginate from a driver of a vehicle applying an accelerator pedal asshown in FIG. 1. In other examples, the engine torque demand mayoriginate from another controller such as a hybrid powertraincontroller. If method 800 judges that the engine torque demand isgreater than a threshold, the answer is yes and method 800 proceeds to830. Otherwise, the answer is no and method 800 proceeds to 812.

At 812, method 800 rotates the turbocharger turbine and compressor in areverse direction. In one example, the reverse direction is a directionopposite to a direction the turbine is driven when exhaust gases impingeon turbine vanes. The turbine may be driven in a reverse direction viaan electrical or hydraulic actuator as shown in FIGS. 2 and 3. Method800 proceeds to 814 after the turbine is driven in a reverse direction.

At 814, method 800 judges whether or not the engine intake manifoldabsolute pressure (MAP) is at a desired level. Since rotating thecompressor in reverse may limit air flow into the intake manifold, MAPis checked to ensure a desired amount of air is entering the engine. IfMAP is determined not to be at a desired level, the answer is no andmethod 800 proceeds to 822. Otherwise, the answer is yes and method 800proceeds to 816.

At 822, method 800 judges whether or not the opening amount of thethrottle is at a threshold amount (e.g., greater than 40% of availablethrottle opening amount). If the throttle opening amount is not at thethreshold opening amount, the answer is no and method 800 proceeds to824. If the throttle opening amount is at the threshold opening amount,the answer is yes and method 800 proceeds to 826.

At 824, the throttle opening amount is adjusted to provide the desiredMAP. If MAP is less than desired MAP, the throttle opening amount isincreased. If MAP is greater than desired MAP, the throttle openingamount is decreased. In one example, the throttle opening amountincrease or decrease may be a function of the difference between desiredMAP and actual or measured MAP. Method 800 returns to 814 after thethrottle opening amount is adjusted.

At 826, method 800 opens the compressor bypass valve to increase MAP. Ifthe compressor bypass valve is a two state valve, the compressor bypassvalve is moved from a closed state to an open state. If the compressorbypass valve is adjustable between more than two states, the compressorbypass valve opening amount may be increased by a predetermined amount.Method 800 proceeds to 824 after the compressor bypass valve state isadjusted.

At 816, method 800 judges whether or not exhaust backpressure is greaterthan a predetermine backpressure. Further, in some examples method 800judges if a predetermined duration since the engine was stopped hasexpired. If the answer to either or both conditions is yes, method 800proceeds to 818. Otherwise, the answer is no and method 800 returns to804.

At 818, method 800 opens the turbocharger waste gate to allow exhaust toflow around the turbine. The waste gate may be electrically orpneumatically opened. Method 800 proceeds to 820 after the waste gate isopened.

At 820, method 800 recirculates exhaust gas from downstream of theturbine (e.g., in the direction of exhaust flow from the engine toatmosphere) or waste gate to the turbine inlet via the reverse rotatingturbine. In some examples, the reverse turbine rotation speed may beadjusted depending on engine operating conditions. For example, theturbine may be rotated in reverse at an increasingly higher speed asengine speed increases. Alternatively, turbine speed may be decreased asengine speed decreases. Method 800 returns to 804 after recirculation ofexhaust gases commences.

In this way, the direction of turbocharger rotation may be controlled sothat exhaust gases may be recirculated about a turbocharger to improveoxidation of exhaust gases. Further, reverse turbine rotation may beceased in response to engine torque demand, time since engine stop, andafter treatment device temperature.

Thus, the method of FIG. 8 provides for a method for operating anengine, comprising: rotating a turbocharger coupled to the engine in afirst direction to increase a time engine exhaust gases are in anexhaust manifold; and rotating the turbocharger in a second direction toincrease engine output torque. The method includes where theturbocharger is operated in the first direction in response to atemperature or a time since the engine was last stopped. The methodincludes where the temperature is an after treatment device temperatureor an engine temperature.

In another example, the method includes where the turbocharger ishydraulically driven in the first direction opposed to a direction ofexhaust flow and where the turbocharger is not hydraulically driven inthe second direction consistent with a direction of exhaust flow. Thus,the hydraulic pump rotating the turbine may be hydraulically driven in asingle direction. The method includes where a turbocharger waste gate isopen while the turbocharger is rotating in the first direction. Themethod includes where a turbocharger compressor bypass valve is openwhile the turbocharger is rotating in the first direction. The methodalso includes where the turbocharger is electrically driven in the firstdirection opposed to a direction of exhaust flow.

In another example, the method of FIG. 8 provides for operating anengine, comprising: recirculating engine exhaust gases that flow througha waste gate in a direction opposed to engine exhaust flow via rotatinga turbocharger turbine in a direction opposed to a direction engineexhaust flow drives the turbocharger turbine. The method furthercomprises ceasing to rotate the turbocharger turbine in the directionopposed to the direction engine exhaust flow drives the turbochargerturbine in response to an increasing engine torque request. The methodfurther comprises compressing air supplied to the engine via theturbocharger in response to the increasing engine torque request. Themethod further comprises closing the waste gate in response to theincreasing torque request.

In another example, the method further comprises ceasing to rotate theturbocharger in the direction opposed to the direction of engine exhaustflow drives the turbocharger turbine in response to a temperature. Themethod includes where the temperature is a temperature of the engine ora temperature of an exhaust after treatment device. The method alsoincludes where the recirculating begins a predetermined amount of timeafter the engine was last stopped.

In another example, the method of FIG. 8 provides for operating anengine, comprising: rotating a turbocharger coupled to the engine in afirst direction to compress air entering an intake manifold; androtating the turbocharger in a second direction to draw exhaust gasesfrom downstream of a waste gate and upstream of an after treatmentdevice to a location upstream of the waste gate. The method includeswhere the waste gate is open while rotating the turbocharger in thesecond direction. The method further comprises adjusting a position of athrottle to achieve a desired MAP in an intake manifold of the engine.In some examples, the method further comprises adjusting a position of acompressor bypass valve in response to the desired MAP. The methodfurther comprises opening the waste gate in response to a predeterminedduration after engine start. The method also includes where the locationupstream of the waste gate is a turbine inlet.

As will be appreciated by one of ordinary skill in the art, the methoddescribed in FIG. 8 may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various steps orfunctions illustrated may be performed in the sequence illustrated, inparallel, or in some cases omitted. Likewise, the order of processing isnot necessarily required to achieve the objects, features, andadvantages described herein, but is provided for ease of illustrationand description. Although not explicitly illustrated, one of ordinaryskill in the art will recognize that one or more of the illustratedsteps or functions may be repeatedly performed depending on theparticular strategy being used.

This concludes the description. The reading of it by those skilled inthe art would bring to mind many alterations and modifications withoutdeparting from the spirit and the scope of the description. For example,single cylinder, I2, I3, I4, I5, V6, V8, V10, V12 and V16 enginesoperating on natural gas, gasoline, diesel, or alternative fuelconfigurations could use the present description to advantage.

1. A method for operating an engine including a turbocharger,comprising: rotating the turbocharger in a first direction to increase atime engine exhaust gases are in an exhaust manifold; and rotating theturbocharger in a second direction different than the first direction toincrease engine output torque.
 2. The method of claim 1, where theturbocharger is operated in the first direction in response to atemperature or a time since the engine was last stopped.
 3. The methodof claim 2, where the temperature is an after treatment devicetemperature or an engine temperature.
 4. The method of claim 1, wherethe turbocharger is hydraulically driven in the first direction opposedto a direction of exhaust flow and where the turbocharger is nothydraulically driven in the second direction consistent with a directionof exhaust flow.
 5. The method of claim 1, where a turbocharger wastegate is open while the turbocharger is rotating in the first direction.6. The method of claim 1, where a turbocharger compressor bypass valveis open while the turbocharger is rotating in the first direction. 7.The method of claim 1, where the turbocharger is electrically driven inthe first direction opposed to a direction of exhaust flow.
 8. A methodfor operating an engine including a turbocharger, comprising:recirculating engine exhaust gases that flow through a waste gate in adirection opposed to engine exhaust flow via rotating a turbochargerturbine in a direction opposed to a direction engine exhaust flow drivesthe turbocharger turbine.
 9. The method of claim 8, further comprisingceasing to rotate the turbocharger turbine in the direction opposed tothe direction engine exhaust flow drives the turbocharger turbine inresponse to an increasing engine torque request.
 10. The method of claim9, further comprising compressing air supplied to the engine via theturbocharger in response to the increasing engine torque request. 11.The method of claim 10, further comprising closing the waste gate inresponse to the increasing engine torque request.
 12. The method ofclaim 8, further comprising ceasing to rotate the turbocharger in thedirection opposed to the direction of engine exhaust flow drives theturbocharger turbine in response to a temperature.
 13. The method ofclaim 12, where the temperature is a temperature of the engine or atemperature of an exhaust after treatment device.
 14. The method ofclaim 8, where the recirculating begins a predetermined amount of timeafter the engine was last stopped.
 15. A method for operating an engineincluding a turbocharger, comprising: rotating the turbocharger in afirst direction to compress air entering an intake manifold; androtating the turbocharger in a second direction to draw exhaust gasesfrom downstream of a waste gate and upstream of an after treatmentdevice to a location upstream of the waste gate.
 16. The method of claim15, where the waste gate is open while rotating the turbocharger in thesecond direction.
 17. The method of claim 16, further comprisingadjusting a position of a throttle to achieve a desired MAP in an intakemanifold.
 18. The method of claim 17, further comprising adjusting aposition of a compressor bypass valve in response to the desired MAP.19. The method of claim 18, further comprising opening the waste gate inresponse to a predetermined duration after engine start.
 20. The methodof claim 15, where the location upstream of the waste gate is a turbineinlet.